Copolymers as thickeners and modifiers for latex systems

ABSTRACT

A thickened aqueous copolymer solution useful for thickening and improving the properties of latex systems comprising a copolymer having as monomeric units: about 79-99 percent of a (meth)acrylic acid salt of sodium, potassium, or ammonium; about 0-20 percent of (meth)acrylic acid; about 0-20 percent of a lower alkyl ester of (meth)acrylic acid; about 1-21 percent of surfactant units selected from the urea reaction product of a monoethylenically unsaturated monoisocyanate with a nonionic surfactant having amine functionality; and about 0-1 percent of a copolymerizable polyethylenically unsatured monomer, said percentages being by weight based on the total weight of monomeric units in said copolymer.

This application is a division of application Ser. No. 07/318,140, filedMar. 2, 1989, which is a continuation-in-part application of copendingU.S. Pat. application Ser. No. 07/046,458, filed May 6, 1987.

BACKGROUND OF THE INVENTION

This invention relates to aqueous copolymer solutions which thicken,modify rheology, stabilize, and otherwise improve the physicalproperties of latex systems and dried film resulting from application oflatex systems to substrates. Of particular importance is the increase intensile strength of dry latex films provided by the addition of thenovel copolymer solutions to latex coating compositions.

Various polymeric materials have been used to thicken latexformulations, improve their mechanical stability, suspend added fillers,and to impart to the formulations the required flow properties andviscosity for application, as well as impart desirable properties todried films and coatings after application. Sodium polyacrylatesolutions resulting from hydrolysis of polymethyl acrylate are used asthickeners, especially in styrene-butadiene latex compositionscontaining calcium carbonate and/or kaolin fillers. Such polyacrylatesolutions are generally supplied at a viscosity low enough for pumpingfrom tank trucks and for rapid mixing into the latex compositions, yetthey are cost effective in thickening latex compositions. They fill aneed in highly-automated upholstery fabric backing and carpet backinglatex adhesive applications.

The alkali reactive type of thickeners, a typical example of which isdisclosed in U.S. Pat. No. 3,070,561, are copolymer emulsions in whichthe copolymer chain contains both ester and carboxyl groups.Neutralization of the carboxyl groups by addition of alkali at ambienttemperature leaves the ester group unaffected, but converts the emulsionto a relatively clear alkali metal or ammonium salt solution of greatlyincreased viscosity.

Recent improvements of alkali reactive thickeners are disclosed in U.S.Pat. Nos. 4,351,754, 4,384,096, 4,514,552, 4,600,761 and 4,616,074. Suchimprovements result from inclusion of certain surfactant monomers inthese associative copolymer thickeners. Such thickeners and theirthickening mechanism are discussed in "Water-Soluble Polymers" by J. E.Glass, Editor, American Chemical Society, Washington, DC (1986). Theseproducts have been found to be useful in only a limited number ofapplications, and have been found to be unsatisfactory in the thickeningof highly-loaded styrene-butadiene latex compositions used as carpet andfabric backing adhesives which generally are applied by automatedmethods in carpet and upholstery mills.

Other types of associative thickeners are described in the patentliterature. Thus, U.S. Pat. No. 3,708,445 discloses aqueous solutioncopolymers of certain surfactant monomers with carboxylic acid monomers,to be useful in thickening latex compositions. U.S. Pat. No. 4,138,381discloses glycol solution terpolymers of certain surfactant monomerswith alkyl (meth)acrylate and carboxylic acid monomers to be useful forthickening aqueous polymeric lattices. U.S. Pat. No. 4,268,641 describescopolymers of certain types of surfactant acrylates withcarboxyl-containing, ethylenically unsaturated hydrocarbons. Suchcopolymers generally are polymerized in an organic liquid from which thecopolymer precipitates. When base-neutralized the copolymers are usefulas thickeners.

In spite of the considerable research activity in this field, the sodiumpolyacrylate solution thickeners resulting from hydrolysis ofpolyacrylic acid esters remain the thickeners of first choice for manytextile back coating and adhesive applications. These polymers,sometimes crosslinked, have continued in use for almost thirty yearswithout substantial change. However, changes in equipment, compoundformulations, and other conditions of use dictate a constant demand forchanges and improvements in these polymer thickeners.

SUMMARY OF THE INVENTION

According to one aspect of this invention new aqueous solutions ofanionic copolymers are provided which are useful for thickening andimproving the characteristics of latex systems.

As another aspect of this invention are provided new dry copolymerproducts useful in the aqueous solutions.

Still a further aspect of this invention provides copolymerizablemonomers and surfactants for use in the copolymer products and aqueoussolutions of the invention.

The invention also provides methods for improving the rheologicalproperties of a latex composition which includes addition to suchcompositions the copolymers or aqueous solutions disclosed by theinvention.

The copolymers of the invention are prepared either by emulsionpolymerization or solvent polymerization. The former procedurepreferably is employed where the copolymers are obtained bycopolymerization of an alkyl ester (meth)acrylate, surfactant monomershaving amine functionality and optionally a small amount of acopolymerizable polyethylenically unsaturated crosslinking monomer.Following polymerization the major portion of the ester groups arehydrolyzed by addition of base to provide acrylate salt groups, wherebythe copolymer goes into solution with resultant thickening of theaqueous system in which the copolymer is present.

However, because of the greater solubility of (meth)acrylic acid, ascompared to the lower alkyl esters thereof, the copolymerization can becarried out in a solvent for the monomers, such as water, where(meth)acrylic acid per se is used as a monomer rather than a lower alkylester thereof. The major portion of the carboxyl groups are neutralizedbefore, during or after polymerization with resulting thickening of theaqueous system.

The copolymers of this invention provide thickeners for latex andlatex-based formulations which significantly improve the overallrheological properties thereof while retaining the proven benefits ofthe hydrolyzed polyacrylate products. An unexpected additional benefitof the present invention is an increase in tensile strength of driedlatex coatings by the inclusion in the lattices of the copolymersolutions of this invention.

Other aspects and advantages of the products and methods of the presentinvention are further discussed in the following detailed description,including preferred embodiments of this invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention thus provides thickened aqueous copolymersolutions useful for thickening and improving the rheology and drytensile strength of latex systems, and the corresponding copolymermonomers. The copolymer solutions contain a copolymer having asmonomeric units:

(A) about 79-99 percent of a (meth)acrylic acid salt of sodium,potassium or ammonium;

(B) about 0-20 percent of (meth)acrylic acid;

(C) about 0-20 percent of a lower alkyl ester of (meth)acrylic acid;

(D) about 1-21 percent of surfactant monomer units selected from ureareaction product of a monoethylenically unsaturated monoisocyanate witha nonionic surfactant of the formula ##STR1## where R₁ is a -C₈ to C₂₀alkyl or C₈ to C₂₀ alkylphenyl or a di(C₈ to C₂₀ alkyl)phenyl, n and mare independently selected from 2 to 4, a and c are independentlyselected from the range of 0 to 100, provided that a+c is within therange of 2 to 100; R₂ and R₃ are independently selected from CH₃ or CH₂CH₃, b and d are independently selected from the rang of 0 to 50,provided that b+d is within the range of 0 to 50; and e is from 1 to 50;wherein the sum of a+c is always greater than the sum of b+d;

(E) about 0-1 percent of a copolymerizable polyethylenically unsaturatedmonomer, said percentages being by weight based on the total weight ofmonomer units.

The copolymers employed in the copolymer solution of this invention areprepared either by emulsion polymerization or by polymerization in asolvent for the monomers. The route selected will depend on thesolubility of the monomers in the reaction medium which preferably iswater. In either instance there results an aqueous copolymer solution.

In a preferred embodiment of the copolymer solution, the copolymer iscomposed of (A) about 92-99 percent (meth)acrylate salt, (B) about 0-8percent (meth)acrylic acid, (C) about 0-8 percent (meth)acrylic loweralkyl ester, (D) about 1-8 percent surfactant monomer units, and (E)about 0.1-0.5 percent crosslinking monomer units.

With regard to component (A) in the aboverecited formula for copolymersolutions, the terms "(meth)acrylic acid" and "(meth)acrylate" as usedin this specification and appended claims refer to acrylic andmethacrylic acid and acrylates and methacrylates, i.e. lower alkylesters of the acids, respectively. In the polymerization reaction bywhich the copolymers are synthesized, either the acids per se and/or thelower alkyl esters may be used as monomers. In either instance, however,the resulting copolymers are treated with base. Where acid monomer unitsper se are present, the major portion of the free carboxyl groups areneutralized to form salts. Preferred neutralizing alkaline reactants aresodium, potassium and ammonium hydroxide.

The conversion of the carboxyl groups into salt groups renders thecopolymers water soluble so that there is formed a substantially clearaqueous solution of substantially increased viscosity.

(Meth)acrylic acid per se may be used as one of the monomers in thepolymerization reaction, and in the copolymer (meth)acrylic acid unitsmay be present up to about 20 percent by failure to neutralize(meth)acrylic acid monomer or hydrolyze lower alkyl (meth)acrylate estermonomer. Preferably, the copolymer does not contain more than about 8percent of (meth)acrylic acid units.

The lower alkyl (meth)acrylates which may be used in thecopolymerization reaction have the general formula

    CH.sub.2 =CYZ

where Y is hydrogen or CH₃ and Z is ##STR2## where R is alkyl containingfrom 1 to 4 carbon atoms. Examples of such nonionic acrylates are methylacrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethylmethylacrylate and butyl methacrylate. Preferred monomers are methyl andethyl (meth)acrylate and mixtures thereof.

The nonionic acrylate units in the copolymer generally comprise up toabout 20 percent of the total monomer units, and preferably about 0-8percent. It can be seen, however, that where a (meth)acrylate isemployed as a monomer in the polymerization reaction a considerablylarger proportion thereof may be present. The percentages given for thenonionic units are those remaining subsequent to alkaline hydrolysis.

Where nonionic (meth)acrylate units are present, the major portionthereof are hydrolyzed by alkali, particularly sodium and potassiumhydroxide whereby the ester groups are converted to alkali metal saltgroups.

The surfactant monomers used in preparing the copolymers according tothis invention are urea reaction products of a monoethylenicallyunsaturated monoisocyanate with certain nonionic surfactants havingamine functionality. A preferred isocyanate for use in forming thecompositions of this invention is alpha, alpha-dimethyl-m-isopropenylbenzyl isocyanate [m-TMI from American Cyanamid Corp.]. Othermonoisocyanates useful in preparing the urea monomers have the formula##STR3## where A is an alkylene group of the formula (CH₂)_(n), where nis from 1 to 20, and Z is CH₂ ═CH-, CH₂ ═C(CH₃)-, or CH₂ ═CH-CH₂ -. Amonoisocyanate of the above formula is isocyanatoethyl methacrylate [DowChemical Corp.]. Nonionic surfactants for reaction with themonoisocyanates to provide urea monomers of the present invention arecharacterized by the presence of a primary amine. Preferred nonionicsurfactants of the formula in (D) above include those in which R₁ isnonylphenyl or octylphenyl or dinonylphenyl or dioctylphenyl. Suchpreferred surfactants are characterized by the above formula where n andm are each 2 and R₂ and R₃ are each CH₃, so that the polymer strand isformed of a series of oxyethylene (EO) and oxypropylene (PO) moieties.Although the EO moieties must always exceed the number of PO moieties,the formula allows for the EO and PO components to be arranged in arandom mixture in the surfactant used in the compositions of the presentinvention. Preferred surfactants of this formula contain a minimum oftwo moles of EO. Practical limitations on the amount of EO and PO in theformula include a maximum of about 100 moles of EO in a surfactant ofthe above formula. Similarly a practical maximum of about 50 moles of POfor surfactants of the above formula is appropriate. In the selection ofa nonionic surfactant according to this invention, the smaller the R₁component, the smaller is the number of EO components in the surfactant,and vice versa.

Such presently preferred embodiments of the present invention employ aclass of surfactants for use in the present invention which have theformula above where R1 is octylphenyl or nonylphenyl, n is from 2 to 4,a is from 3 to 30, R₂ is CH₃ or CH₂ CH₃, b is from 0 to 10, c, d and mare 0, and e is 1. An example of a suitable nonionic surfactant whichfalls within this formula and can be reacted with the monoisocyanatesaccording to this invention is nonylphenoxy poly[(oxyethylene)₉.5(oxypropylene)₂ ] amine [Texaco, Inc.].

Other preferred embodiments of the present invention employ a class ofsurfactants for use in the present invention which have the formula of(D) above where R1 is octylphenyl or nonylphenyl, a and d are 0, b isfrom 1 to 10, m is from 2 to 4, c is from 3 to 30, R₃ is CH₃ or CH₂ CH₃,and e is 1. An example of a suitable nonionic surfactant which fallswithin this formula and can be reacted with the monoisocyanatesaccording to this invention is nonylphenoxy poly[(oxypropylene)₂(oxyethylene)₉.5 ] amine.

Other surfactants falling with the formula of (D) above may also beemployed in the compositions of the present invention.

These surfactant reactants for the most part are commercially available.By employing a suitable stannous catalyst, the condensation may becarried out at a relatively low temperature, e.g. 40° C. to 60° C. andessentially quantitative yields obtained. No by-products are formed, andthus purification of the product is unnecessary. This feature of thereaction is important in determining and controlling the amount of boundsurfactant monomer present in the copolymer, whereby copolymerreproducibility is readily accomplished.

Preferably the nonionic surfactant monomer comprises about 1 to about 21percent of the copolymer, the percentage being by weight based on totalweight of monomer units. The particularly preferred amount of suchnonionic surfactant monomer is from about 1 to about 8 percent.

Preparation of the urea surfactant monomers is described in detail inExample I. General conditions for the reaction are also described in thereferences cited above in the prior art discussion. Such procedures arewell known, and the details thereof are not to be construed as limitingthis invention.

Also employed as an optional component in the copolymer solutions of thepresent invention is a small amount, such as 0 to 1 percent, preferably0.1 to 0.5 percent, of a polyethylenically unsaturated crosslinkingmonomer. This monomer may be added as a crosslinking agent for thecopolymers. Suitable monomers for this use include diallyl phthalate,vinyl crotonate, allyl methacrylate, divinyl benzene, and the like.

The above-described components of the copolymer solutions of thisinvention are copolymerized as follows. When (meth)acrylic acid estermonomers are used as the major source of carboxylic monomer units in thecopolymers, the copolymerization preferably is carried out by ordinaryemulsion polymerization techniques, at a concentration of monomer inwater of about 16%. Typical performance of this reaction is described inExample II. Conventionally, there is considerable latitude in choice ofreaction temperature, initiator system, and emulsifier(s) for thisreaction. Choice of emulsifier, in particular, can be used to varyproduct properties and may be selected by one of skill in the art.Pre-emulsion of monomers is useful in minimizing coagulum formation.Conditions for basic hydrolysis of the copolymer emulsion are notcritical, provided that the hydrolysis is continued until the base isconsumed and a solution is formed. The amount of base should besufficient so that in the copolymer there are at least 79% by weight of(meth)acrylic acid salt units. It is good practice to add the baseslowly to the copolymer emulsion which preferably has been cooled toambient temperature with good stirring. Preferred conditions forcarrying out the hydrolysis are a reaction temperature of 90° to 95° C.,with a 4 to 16 hour cook time. If a volatile base is chosen, thehydrolysis may be conducted under pressure. It is convenient to keep thealcohol liberated on hydrolysis in the resulting thickened aqueoussolution of copolymer product, for the alcohol has little effect onproduct properties. However, the alcohol can optionally be removed bydistillation if the end use application of the composition requiresabsence of alcohol.

Solution polymerization is preferred when monomer salt units (A) of thecopolymer solution result from neutralization of the acid per se. Aconvenient technique is the concurrent feeding of initiator solution andof a mixture of the monomers to a reactor containing water held at 40°to 100° C. Such common expedients as nitrogen sparging, and the use ofredox initiating systems, metal activators, and chain length regulatorsmay be employed.

The degree of hydrolysis or neutralization in preparation of thecopolymers may be chosen within wide limits, subject to end userequirements of compatibility and effectiveness in the formulation to bethickened and provided that the copolymers contain at least 79%, byweight, of carboxylic acid salt units. Neutralized copolymer solutionsmay have a pH as low as 6. Generally, optimum thickening performance isachieved when the copolymer solution has a pH range of 8 to 12.

The average molecular weights of copolymers are estimated to be betweenabout 100,000 and 5,000,000. Preferred copolymers have an averagemolecular weight of from about 200,000 to 1,000,000.

Generally the copolymer solutions of this invention will have a solidscontent of from about 8% to about 20%. The amount of copolymer solutionadded to a latex to thicken it and improve its rheological propertiespreferably provides from about 0.2 to about 3 parts by weight ofcopolymer, dry basis, based on 100 dry parts of latex. The copolymerproducts may be dried, to reduce shipping costs, or to remove solvent,aqueous or organic.

The following examples are provided for illustration only, and are notintended to limit the scope of this invention in any way.

EXAMPLE I Preparation of a surfactant urea monomer

264 grams (0.352 mole) of nonyl phenoxy poly[(oxyethylene)₉.5(oxypropylene)₂ ] amine [Texaco, Inc.]were slowly heated in a 1-literreactor fitted with a thermometer, stirrer, reflux condenser, andheating mantle. When the temperature of the amine reached 40° C., 0.69 gof the monomethyl ether of hydroquinone and 0.67 g of stannous octoatewere added. The solution was then heated to 50° C. and 69.8 g (0.347mole) of alpha, alpha-dimethyl-m-isopropenyl benzyl isocyanate [AmericanCyanamid Corp] were added dropwise from an addition funnel over atwo-hour period while the reaction mixture was maintained at 55° to 60°C. The reaction mixture was then cooked 1 hour at 60° C. The finalproduct after cooling was a viscous solution.

Additional surfactant urea monomers of the present invention used in thefollowing examples and tables were made by substantially the same methoddescribed above in Example I.

EXAMPLE II Preparation of a copolymer of the invention by emulsionpolymerization and hydrolysis

A mixture of 345 g water, 2.8 g of ethoxylated nonyl phenol (IgepalCO-990, GAF Corporation), and 0.37 g soda ash were charged to a 1-literreactor fitted with a thermometer, stirrer, condenser, and heatingmantle.

A pre-emulsion of monomers was prepared in a beaker by mixing 182 gwater, 2.8 g of monomer prepared according to Example I, 8.0 gethoxylated nonyl phenol, 46.4 g (0.539 eq.) methyl acrylate, 46.4 g(0.463 eq.) ethyl acrylate, and 0.20 g divinyl benzene.

The reactor charge was heated to 80° C. and 0.57 g potassium persulfatewas added. The monomer pre-emulsion and 12 g of a 5 percent solution ofpotassium persulfate were added from addition funnels at constant ratesover 90 minutes while maintaining the reaction mixture at 80° C. Thelatex formed was cooked at 88° C. for 1 hour, 100 g water were added,and the mixture was cooled to 30° C.

145 g of a 25 percent solution of sodium hydroxide (0.906 eq.) wereadded to the latex with mixing over 10 minutes. The mixture was heatedto 90° to 95° C. and cooked at that temperature for 16 hours.

The product was a clear solution having a solids content of 13.0percent, a viscosity of 12,000 cps, and a pH of 8.9.

EXAMPLE III Preparation of a copolymer solution by aqueous solutionpolymerization and neutralization

To a 1.5 liter reaction flask equipped with a thermometer, mechanicalstirrer, heating mantle, nitrogen inlet and condenser, were charged 920g of city water, 178.2 g of acrylic acid and 2.7 g of the urea monomerof Example I.

The reactor charge was heated to 40° C. and purged with nitrogen. At 40°C., 1.08 g of an 8.26 percent aqueous solution of ammonium persulfatewere added followed after 1 minute by addition of 0.54 g of a 4.3%solution of sodium metabisulfite. An exotherm was noted after a fewminutes. The temperature then rose to 70° C. to 80° C. within 10minutes. The resulting polymer was then held at 70° C. to 80° C. for 1hour. The product was cooled and a 50 percent sodium hydroxide solutionwas added to increase the pH to 8 to 9.

The procedures of Examples II and III were used to prepare the copolymersolutions (CS) in Table A. The CS numbers are arbitrary designations.For all examples the copolymerizable surfactant monomer (CPS) was theproduct described in Example I above.

                                      TABLE A                                     __________________________________________________________________________                                 Weight % Monomer Units in                                                     Copolymer After Hydrolysis                                                    or Neutralization                                                                                % Hydrolysis                                                                  as mole                       Weight % Monomer as Charged     Residual        % NaOH on                     CS*                                                                              CPS   Acrylic                                                                            Methyl                                                                             Ethyl                                                                              Divinyl MA/EA**                                                                             Sodium                                                                             Divinyl                                                                            Lower Acrylic                 No.                                                                              No.                                                                              CPS                                                                              Acid Acrylate                                                                           Acrylate                                                                           Benzene                                                                            CPS                                                                              Total Acrylate                                                                           Benzene                                                                            Esters                        __________________________________________________________________________    8  3  2.9                                                                              0    97   0    0.20 2.7                                                                              12.3  85   0.18 86                            10 3  1.5                                                                              99   0    0    0.0  1.5                                                                              0.0   99   0.00  98%                                                                          (neutralization)              248                                                                              3  10 0    45   45   0.19 10 11    79   .19  80                            249                                                                              3  15 0    42.5 42.5 0.19 15 6     79   .19  80                            250                                                                              3  20 0    40   40   0.19 20 1     79   .19  80                            117                                                                              3  2.9                                                                              0    48   48   0.20 3.0                                                                              4.7   92   .21  91                            __________________________________________________________________________     *Copolymer Solution                                                           **MA refers to methyl acrylate, and EA refers to ethyl acrylate.         

EXAMPLE IV The Properties of the Above-Described Copolymers andSolutions

The rheological properties that the copolymer solutions of thisinvention contribute to a latex coating system were evaluated using atypical carpet coating formulation. Such carpet coatings consist of alatex binder with 100 to 800 parts by weight of filler, usually calciumcarbonate. Also, such type coatings usually contain a frothing aid tofacilitate the aeration of the coatings. The viscosities of the coatingsare modified with a thickener, such as a copolymer solution of thisinvention, to achieve the desired rheological properties.

The properties which exemplary copolymer solutions of this invention (CS#8 and 10 from Table A) contribute to a carpet coating system areprovided in Table B. The coating system used in this evaluationconsisted of 100 dry parts of styrene butadiene latex (ReicholdChemical, Inc. Latex 69700), 600 dry parts of calcium carbonate filler,and 1.2 parts of foaming agent (Stanfax 234) [Standard Adhesives Co.,Dalton, GA]. The total solids of the composition was adjusted to 83percent with water. The several tests employed in determining theproperties of the coating system are described hereinbelow.

The copolymer solutions of this invention were used to increase theviscosity of the above-described coating formulation to an initialviscosity of 14000 cps ±400, as measured with RVT Brookfield viscometerat 20 rpm.

The coatings were left undisturbed for 24 hours before the staticviscosity was measured. The coatings were then agitated for 5 minutesbefore the restir viscosity was measured. If there is a substantialincrease in these viscosities, the coating will be difficult to transferand penetration of the coating into a substrate will be adverselyaffected. A decrease in these viscosities does not interfere withtransfer, but the penetration into the substrate may be excessiveresulting in excessive usage of coating material and/or defectivecarpet.

The shear rate viscosities, also measured with a RVT Brookfieldviscometer, give a good indication of the pseudoplastic properties ofthe novel copolymer solutions to the coating system. Viscosity readingsare taken at 1, 20 and 50 rpm which give three shear rates. The greaterthe difference between the low and high shear viscosities, the morepseudoplastic the coating will be. A certain amount of this type of flowis necessary to achieve the proper flow on the substrate. Thepseudoplastic flow of coating formulations containing the copolymersolutions of this invention is well within the operating range ofcoating equipment.

The yield testing as used in the carpet industry and discussed here isnot really a measure of yield point in rheological terms. It is a stressrelaxation determination which gives an indication of coating flow atvery low shear rates. In the test a Brookfield viscometer is used (amodel RVT with #3 spindle was used), and the spindle is turned by handto its limit of a 100 dial reading while in the coating.

The spindle is held in this position for 10 seconds. This is importantbecause of the viscoelasticity of many coatings. After the 10 secondhold, the spindle is released and readings are taken at various timeperiods. A one minute reading has become somewhat standard in the carpetindustry. This stress relaxation test gives a good indication of thecoating's ability to penetrate into a substrate, and if the yield ishigh, the coating's high ride property. The copolymer solutions of thisinvention demonstrate a useful range of coating placement properties.

Since most coatings regardless of type are heated to speed the curingprocess, the coating viscosities at elevated temperatures are importantto the quality of the final product. This type of testing is referred toas heat stability. The coating is heated under agitation in a bath tovarious temperatures which depend on the coating application equipments,and viscosities are recorded. The temperatures evaluated here are 100°F., 140° F., and 160° F. (37.8°, 60° and 71° C.) which are useful forcarpet type coatings.

If the viscosities increase as the temperature increases, the coatingswill ride high once the substrate I0 is in the oven. If the viscositiesdecrease as the temperature increases, the coatings will penetrate intothe substrate during initial cure. The tests show that the copolymersolutions of this invention maintain a useful range of heat stability.

Many coatings are aerated or frothed before application to a substrate.The frothed viscosity gives another important rheological property of acoating. The coatings are frothed in a Hobart to a density of 800 gramsper liter. A Brookfield viscosity is recorded using the RVT with a #6spindle. This viscosity controls the placement of the coating prior tocuring. The copolymer solution of this invention demonstrates usefulranges of frothed viscosities as shown by the data in Table B.

Latex films were used for tensile testing. The films consisted of 100dry parts of a styrene butadiene latex, and 0.5 parts of a thickener.This material was drawn down on teflon sheet using a bird bar (0.030").The resulting film was air-dried at room temperature for 12 hours,removed from the teflon plate and oven-cured for 10 minutes at 140° C.The tensile pulls were made with a 1/2" dumbbell.

                                      TABLE B*                                    __________________________________________________________________________       Parts                                                                         Thickener                                                                     per                                                                           100 parts   24 hr.               Yield            Frothed                  CS Dry Latex                                                                           Viscosity                                                                           Static                                                                            Restir                                                                             Shear Rate  #3 RV                                                                              Heat Stability                                                                            Viscosity                                                                          Tensile             No.                                                                              Wet                                                                              Dry                                                                              CPS   CPS CPS  1 rpm                                                                             20 rpm                                                                            50 rpm                                                                            1 min                                                                              100° F.                                                                    140° F.                                                                    160° F.                                                                    CPS  PSI(a)              __________________________________________________________________________    8  4.00                                                                             0.55                                                                             14300 13000                                                                             11700                                                                               85000                                                                            13500                                                                             7800                                                                              35   18000                                                                             19000                                                                             18250                                                                             13000                                                                              2409                10 8.72                                                                             1.24                                                                             13800 15200                                                                             12100                                                                              13800                                                                             15200                                                                             8320                                                                              72   14000                                                                             13300                                                                             13600                                                                             21400                                                                              2158                __________________________________________________________________________     *Latex consisted of 100 dry parts styrene/butadiene copolymer, 600 dry        parts ground calcium carbonate, 1.2 dry parts forming agent. Total solids     content of the latex 83%, adjusted with water                                 (a)unloaded latex films using Dow RAP 200 latex.                         

Additional thickeners were developed with the copolymer solutionsdesignated CS#248, 249 and 250 substantially as described above for CS#8and 10.

The physical properties of the copolymer solutions alone, specificallytotal solid percentages, pH and viscosity were measured and shown inTable C.

                  TABLE C                                                         ______________________________________                                                     MCB 248 MCB 249   MCB 250                                        ______________________________________                                        Total Solids, %                                                                              4.76      4.31      4.63                                       pH             10.1      11.8      12.5                                       As-Is Viscosity, cps                                                                         15600     21000     45000                                      RVT, 20 rpm, sp 6                                                             ______________________________________                                    

The physical characteristics, tensile strength and percent elongation ofthese compositions as thickeners in one typical coating composition weremeasured at a cure time of 10 minutes at 130° C. and the resultsillustrated in Table D below. The cure time of 10 minutes isrepresentative of actual coating operations. Additional cure times aresimply not economic in the modern production plant. The compositions ofthe present invention provide enhanced tensile strength to coatingcompositions which are of significant economic value to coating andcarpeting manufacturing processes.

                  TABLE D                                                         ______________________________________                                        RIC 69727 Latex dry                                                                          100       100       100                                        Filler D-70    50        50        50                                         Thickener Examples                                                                           MCB 248   MCB 249   MCB 250                                    Thickener TSC  4.760     4.310     4.630                                      Thickener wet parts                                                                          16.900    21.900    19.400                                     Thickener dry parts                                                                          0.804     0.944     0.898                                      #5 @ 20 rpm    9700      9000      9000                                       Initial Viscosity                                                             24 Hours Before Stir                                                                         9850      9350      9100                                       24 Hours After Stir                                                                          8400      7800      7450                                       Tensile PSI                                                                             10 min   501.2     580.1   641.9                                    % Elongation                                                                            cure at  489.0     498.0   569.0                                              130° C.                                                      ______________________________________                                    

Additional characteristics of these compositions of the presentinvention in another coating composition are reported in Table E below.The results demonstrate that compositions of this invention arecharacterized by an appropriate viscosity and stability for coating useand are thus of value in meeting the practical needs of an adhesivesystem, particularly for carpet coatings. These products demonstrategreat resistance to movement in frothed compound which relates inpractical use to coat weight control. This feature benefits themanufacturer in instantly improved adhesive economics beyond theprevious norm in the traditional industrially accepted manufacturingprocesses.

                  TABLE E                                                         ______________________________________                                                    dry  wet    dry     wet  dry  wet                                 ______________________________________                                        RIC 69727 Latex                                                                             100    177    100   177  100  177                               Filler D-70   600    600    600   600  600  600                               Water         --     65     --    65   --   65                                Froth Aid SCT 756                                                                           1.5    5.0    1.5   5.0  1.5  5.0                               Thickener Examples                                                                          MCB 248   MCB 249    MCB 250                                    Thickener wet parts                                                                         19.000    27.300     28.300                                     Thickener dry parts                                                                         0.904     1.180      1.310                                      SP5 20 rpm Initial                                                                          14,200    14,500     14,000                                     Viscosity                                                                     24 Hours Before Stir                                                                        23400     23200      24700                                      24 Hours After Stir                                                                         15700     13900      16800                                      Froth Time    1:36      1:21       1:30                                       Cup Weight g/3 oz                                                                           70.8      75.5       69.3                                       Froth Viscosity                                                                             24200     21800      19900                                      pH of Compounds                                                                             8.88      8.95       9.06                                       ______________________________________                                    

Numerous modifications and variations in practice of the presentinvention are expected to occur to those of skill in the art. Forexample, other nonionic primary amine surfactants falling within thedescribed formulae are expected to function appropriately in thecopolymer products, solutions and methods of this inventions.Additionally other components analogous to those described herein, e.g.,other isocyanates, are also expected to be selected by one of skill inthe art and function according to the invention. Such modifications andvariations are believed to be encompassed by the scope of the appendedclaims.

What is claimed is:
 1. A dry copolymer product useful for thickening andimproving the rheology and dry tensile strength of latex systemscomprising a copolymer having as monomeric units:(A) about 79-99 percentof (meth)acrylic acid salt of sodium, potassium or ammonium; (B) about0-20 percent of (meth)acrylic acid; (C) about 0-20 percent of loweralkyl ester of (meth)acrylic acid; (D) about 1-21 percent of surfactantmonomer which is the urea reaction product of a monoethylenicallyunsaturated monoisocyanate with a nonionic surfactant having the formula##STR4## where R₁ is a C₈ to C₂₀ alkyl or a C₈ to C₂₀ alkylphenyl or adi(C₈ to C₂₀ alkyl)phenyl, n and m are independently selected from 2 to4, a and c are independently selected from the range of 0 to 100,provided that a+c is within the range of 2 to 100; R₂ and R₃ areindependently selected from CH₃ or CH₂ CH₃, b and d are independentlyselected from the range of 0 to 50, provided that b+d is within therange of 0 to 50; and e is form 1 to 50; wherein the sum of a+c isalways greater than the sum of b+d; (E) about 0-1 percent ofcopolymerizable polyethylenically unsaturated monomer, said percentagesbeing by weight based on the total weight of monomeric units in saidcopolymer.
 2. A dry copolymer product according to claim 1 wherein thenonionic surfactant of (D) has the formula ##STR5## where R₁ isoctylphenyl, di-octylphenyl, nonylphenyl or di-nonylphenyl, n or m is aninteger from 2 to 4, a and c are from 3 to 30, R₂ and R₃ are CH₂ CH₃,and b is from 0 to
 10. 3. A dry copolymer product according to claim 1in which said copolymer is composed of (a) about 92-99 percent(meth)acrylate salt units, (B) about 0-8 percent (meth)acrylic acidunits, (C) about 0-8 percent (meth)acrylic lower alkyl ester units and(E) about 0.1-0.5 percent crosslinking monomer units.
 4. A dry copolymerproduct according to claim 1 wherein said (meth)acrylic acid salt units(A) comprise sodium acrylate units and said surfactant monomer units arethe urea reaction product of alpha-, alpha-, dimethyl-m-isopropenylbenzyl isocyanate with said non-ionic surfactant.
 5. The method ofimproving the rheological properties of a latex composition whichcomprises adding thereto from about 0.5 to about 2.5 parts by weight,dry basis of a copolymer of claim 2, in aqueous solution, based on 100dry parts of latex, said solution having a solids content of from about10 to about
 15. 6. The method of improving the rheological properties ofa latex composition which comprises adding thereto from about 0.5 toabout 2.5 parts by weight, dry basis of a copolymer of claim 3, inaqueous solution, based on 100 dry parts of latex, said solution havinga solids content of from about 10 to about
 15. 7. A method of improvingthe rheological properties and dry tensile strength of a latexcomposition which comprises adding thereto from about 0.2 to about 3parts by weight, dry basis, of a copolymer having as monomeric units:(A)about 79-99 percent of a (meth)acrylic acid salt of sodium, potassium orammonium; (B) about 0-20 percent of (meth)acrylic acid; (C) about 0-20percent of a lower alkyl ester of (meth)acrylic acid; (D) about 1-21percent of surfactant monomer which is the urea reaction product of amonoethylenically unsaturated monoisocyanate with a nonionic surfactanthaving the formula ##STR6## where R₁ is a C₈ to C₂₀ alkyl or a C₈ to C₂₀alkylphenyl or a di(C₈ to C₂₀ alkyl)phenyl, n and m are independentlyselected from 2 to 4, a and c are independently selected from the rangeof 0 to 100, provided that a+c is within the range of 2 to 100; R₂ andR₃ are independently selected from CH₃ or CH₂ CH₃, b and d areindependently selected from the range of 0 to 50, provided that b+e iswithin the range of 0 to 50; and e is from 1 to 50; wherein the sum ofa+c is always greater than the sum of b+d; (E) about 0-1 percent ofcopolymerizable polyethylenically unsaturated monomer, said percentagesbeing by weight based on the total weight of monomeric units in saidcopolymer; in aqueous solution, based on 100 dry parts of latex, saidsolution having a solids content of from about 8 to about 20.